1. Field of the Invention
The present invention is directed to a gas diffusion layer arrangement for a fuel cell.
2. Description of the Related Art
FIG. 6 is an exploded cross-sectional view showing a basic configuration of an element cell of a solid polymer type fuel cell which is one embodiment of the conventional fuel cell. A cell is constructed by bonding an air electrode (cathode) side catalyst layer 2 containing a noble metal (mainly platinum) and a fuel electrode (anode) side catalyst layer 3 respectively to main faces at the both sides of a solid polymer electrolyte film 1. An air electrode side gas diffusion layer 4 and a fuel electrode side gas diffusion layer 5 are disposed respectively in opposition to the air electrode side catalyst layer 2 and the fuel electrode side catalyst layer 3. Thereby, an air electrode 6 and a fuel electrode 7 are configured respectively. These gas diffusion layers 4 and 5 function to pass an oxidant gas and a fuel gas, respectively, and, at the same time, to make the current flow to the outside. Then, an element cell 11 is configured by providing a gas passage 8 for reaction gas communication facing the cell, and pinching with a set of separators 10 provided with a cooling water passage 9 for cooling water communication on the opposed main faces and formed of an electrically conductive and gas impermeable material.
FIG. 7 is a cross-section view showing a basic composition of a solid polymer type fuel cell stack. A number of element cells 11 are stacked, sandwiched by a collector plate 12, an insulator plate 13 for of electric insulation and heat insulation, and a tightening plate 14 for maintaining the stacked state by applying a load, and tightened by means of bolts 15 and nuts 17 a tightening load being applied by a plate spring 16.
The solid polymer electrolyte film 1 has a proton exchange group at the molecular level, and functions as a proton electrically conductive electrolyte, as the specific resistance becomes equal to or less than 20 Ω cm2, if the water content is saturated. Thus, because the solid polymer electrolyte film 1 functions as a proton electrically conductive electrolyte by containing water, in the solid polymer type fuel cell, a method to operate by supplying each element cell 11 with reaction gas saturated with water vapor is adopted.
When the fuel electrode 7 is supplied with a fuel gas containing hydrogen, and the air electrode 6 is supplied with an oxidant gas containing oxygen, the fuel cell electrode reaction for decomposing hydrogen molecular into hydrogen ions and electrons takes place in the fuel electrode 7 and the following electric chemical reaction occurs for generating water from oxygen, hydrogen ions and electrons in the air electrode 6, respectively, where the load is supplied with power by electrons moving in an external circuit from the fuel electrode towards the air electrode, resulting in the production of water at the air electrode side.                Fuel electrode; H2→2H++2e−(fuel electrode reaction)        Air electrode; 2H++(½)O2+2e−→H2O (air electrode reaction)        Whole; H2+(½)O2+→H2O        
Thus, in addition to water produced by the reaction at the air electrode 6 side, water moving from the fuel electrode 7 side to the air electrode 6 side along with the movement of hydrogen ions also results.
Therefore, the gas diffusion layers 4 and 5 are required to assure the functions of 1) supplying the catalyst layer evenly with reaction gas to be supplied, 2) conducting the current to the outside, 3) controlling satisfactorily the supply/discharge of reaction produced water and moving water, or other functions.
Consequently, in the prior art, as gas diffusion layer 4 and 5, carbon paper, carbon cloth or other electrically conductive porous material, the electrically conductive porous material subjected to the water repellent treatment, or material coated with a mixture formed of carbon powder and water repellent filler on the electrically conductive porous material have been used.
However, the conventional gas diffusion layer is expensive and, moreover, in case of carbon paper, it has been manufactured in batch because its mechanical strength is low, making difficult to form continuously with respect to the electrode manufacturing, it resulting in poor productivity.